Indexing resources for transmission of acknowledgement signals in multi-cell tdd communication systems

ABSTRACT

Methods and apparatus are described for a User Equipment (UE) to determine a set of resources available for transmitting an acknowledgement signal in an UpLink (UL) Component Carrier (CC) in response to reception of multiple DownLink (DL) Scheduling Assignments (SAs) transmitted from a base station with each DL SA being associated with a respective DL CC. The UL CC and a first DL CC establish a communication link when the UE is configured for communication over a single UL CC and a single DL CC.

PRIORITY

This application is a Continuation application of U.S. patentapplication Ser. No. 14/172,504, filed in the U.S. Patent and TrademarkOffice on Feb. 4, 2014, now U.S. Pat. No. 9,510,366, issued on Nov. 29,2016, which is a Continuation application of U.S. patent applicationSer. No. 13/077,046, filed in the U.S. Patent and Trademark Office onMar. 31, 2011, now U.S. Pat. No. 8,644,199, issued on Feb. 4, 2014,which claims priority under 35 U.S.C. §119(e) to U.S. ProvisionalApplication No. 61/319,524, which was filed on Mar. 31, 2010, thecontents of each of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention is directed generally to wireless communicationsystems and, more specifically, to the transmission of acknowledgementsignals in an UpLink (UL) of a communication system using time divisionmultiplexing (TDM).

2. Description of the Art

A communication system includes a DownLink (DL), conveying transmissionsof signals from a Base Station (BS or NodeB) to User Equipments (UEs),and the UL, conveying transmissions of signals from UEs to the NodeB. AUE, also commonly referred to as a terminal or a mobile station, may befixed or mobile, such as a wireless device, a cellular phone, a personalcomputer device, etc. A NodeB is generally a fixed station and may alsobe referred to as a Base Transceiver System (BTS), an access point, orsome other similar terminology.

The UL supports transmissions of data signals carrying informationcontent, control signals providing information associated with thetransmission of data signals in the DL, and Reference Signals (RSs),which are also commonly referred to as pilot signals. The DL alsosupports transmissions of data signals, control signals, and RSs.

UL data signals are conveyed through a Physical Uplink Shared CHannel(PUSCH). DL data channels are conveyed through a Physical DownlinkShared CHannel (PDSCH). In the absence of PUSCH transmission, a UEconveys Uplink Control Information (UCI) through a Physical UplinkControl CHannel (PUCCH). In the presence of PUSCH transmission, a UE mayconvey UCI together with data information through the PUSCH.

DL control signals may be of broadcast or UE-specific nature.UE-specific control signals can be used, for example, to provideScheduling Assignments (SAs) to a UE for PDSCH reception (DL SAs) orPUSCH transmission (UL SAs). The NodeB transmits an SA using a PhysicalDownlink Control CHannel (PDCCH).

UL control signals include ACKnowledgement signals associated with aHybrid Automatic Repeat reQuest (HARQ) process (HARQ-ACK signals) andare typically transmitted in response to PDSCH receptions.

FIG. 1 illustrates a conventional PUCCH structure for HARQ-ACK signaltransmission in a Transmission Time Interval (TTI), which consists ofone sub-frame.

Referring to FIG. 1, a sub-frame 110 includes two slots 120. Each slot120 includes N_(symb) ^(UL) symbols for transmitting HARQ-ACK signals130 and RSs 140, which enable coherent demodulation of the HARQ-ACKsignals. Each symbol further includes a Cyclic Prefix (CP) to mitigateinterference due to channel propagation effects. The transmission in thefirst slot may be at a different part of an operating BandWidth (BW)than in the second slot in order to provide frequency diversity. Theoperating BW includes frequency resource units that are referred to asPhysical Resource Blocks (PRBs). Each PRB includes N_(sc) ^(RB)sub-carriers, or Resource Elements (REs), and a UE transmits HARQ-ACKsignals and RSs over one PRB 150.

FIG. 2 illustrates the HARQ-ACK signal transmission in a sub-frame slotfor the PUCCH structure in FIG. 1.

Referring to FIG. 2, b HARQ-ACK bits 210 modulate a Constant AmplitudeZero Auto-Correlation (CAZAC) sequence 230 in modulators 220, forexample, using Binary Phase Shift Keying (BPSK) or Quadrature PhaseShift Keying (QPSK) modulation. The modulated CAZAC sequence is thentransmitted after performing an Inverse Fast Fourier Transform (IFFT).Each RS is transmitted through the non-modulated CAZAC sequence afterperforming an IFFT 240.

FIG. 3 illustrates a transmitter block diagram for the PUCCH structurein FIG. 1.

Referring to FIG. 3, the HARQ-ACK information modulates a CAZAC sequence310 which, without modulation, is also used for the RS. A controller 320selects the first and second PRBs for transmission of the CAZAC sequencein the first and second slots of the PUCCH sub-frame and controls asub-carrier mapper 330. The sub-carrier mapper 330 maps the first andsecond PRBs to the CAZAC sequence according to the control signal fromthe controller 320, respectively, an IFFT 340 performs IFFT, and aCyclic Shift (CS) mapper 350 cyclically shifts the output of the IFFT340. Finally, the CP inserter 360 inserts a CP to the signal output bythe CS MAPPER 350, and a filter 370 performs time windowing to generatea transmitted signal 380. A UE is assumed to apply zero padding in REsthat are not used for its signal transmission and in guard REs (notshown). Moreover, for brevity, additional transmitter circuitry such asdigital-to-analog converter, analog filters, amplifiers, and transmitterantennas as they are known in the art, are not shown.

FIG. 4 illustrates a receiver block diagram for the PUCCH structure inFIG. 1.

Referring to FIG. 4, an antenna receives an analog signal and afterpassing through further processing units, e.g., filters, amplifiers,frequency down-converters, and analog-to-digital converters (not shown)a digital received signal 410 is then filtered by a filter 420 and theCP is removed by a CP remover 430. Subsequently, the CS is restored byCS demapper 440, a Fast Fourier Transform (FFT) is applied by FFT 450, acontroller 465 selects the first and second PRBs of the signaltransmission in the first slot and second slots, respectively, andcontrols a sub-carrier demapper 460. The sub-carrier demapper 460 demapsthe first and second PRBs according to the control signal from thecontroller 465, and the signal is correlated by multiplier 470 with areplica of the CAZAC sequence 480. The output 490 can then be passed toa channel estimation unit, such as a time-frequency interpolator, for anRS, or to a detection unit for the CAZAC sequence modulated by HARQ-ACKbits.

Different CSs of the same CAZAC sequence provide orthogonal CAZACsequences and can be allocated to different UEs to achieve orthogonalmultiplexing of HARQ-ACK signal transmissions in the same PRB. If T_(s)is the symbol duration, a number of such CSs is approximately └T_(s)/D┘,where D is the channel propagation delay spread, and └ ┘ is the floorfunction which rounds a number to its immediately lower integer.

In addition to orthogonal multiplexing of HARQ-ACK signals fromdifferent UEs in the same PRB using different CSs of a CAZAC sequence,orthogonal multiplexing can also be achieved in the time domain usingOrthogonal Covering Codes (OCC).

For example, in FIG. 2, the HARQ-ACK signal can be modulated by alength-4 OCC, such as a Walsh-Hadamard (WH) OCC, while the RS can bemodulated by a length-3 OCC, such as a DFT OCC (not shown). Accordingly,the multiplexing capacity is increased by a factor of 3 (determined bythe OCC with the smaller length). The sets of WH OCCs, {W₀, W₁, W₂, W₃},and DFT OCCs, {D₀, D₁, D₂}, are respectively

$\begin{bmatrix}W_{0} \\W_{1} \\W_{2} \\W_{3}\end{bmatrix} = {{\begin{bmatrix}1 & 1 & 1 & 1 \\1 & {- 1} & 1 & {- 1} \\1 & 1 & {- 1} & {- 1} \\1 & {- 1} & {- 1} & 1\end{bmatrix}\mspace{14mu} {{and}\mspace{14mu}\begin{bmatrix}D_{0} \\D_{1} \\D_{2}\end{bmatrix}}} = {\begin{bmatrix}1 & 1 & 1 \\1 & ^{{- j}\; 2{\pi/3}} & ^{{- j}\; 4{\pi/3}} \\1 & ^{{- j}\; 4{\pi/3}} & ^{{- j}\; 2{\pi/3}}\end{bmatrix}.}}$

Table 1 presents a mapping for the PUCCH resource n_(PUCCH) used forHARQ-ACK signal and RS transmission to an OCC n_(oc) and a CS α assuming6 CS per symbol and a length-3 OCC. If all resources within a referencePUCCH PRB are used, the resources in the next PRB immediately followingthe reference PUCCH PRB can be used.

TABLE 1 PUCCH Resource Mapping to OCC and CS. OCC n_(oc) for HARQ-ACKand for RS CS α W₀, D₀ W₁, D₁ W₃, D₂ 0 n_(PUCCH) = 0 n_(PUCCH) = 6 1n_(PUCCH) = 3 2 n_(PUCCH) = 1 n_(PUCCH) = 7 3 n_(PUCCH) = 4 4 n_(PUCCH)= 2 n_(PUCCH) = 8 5 n_(PUCCH) = 5

The SAs in the PDCCH are transmitted in elementary units that arereferred to as Control Channel Elements (CCEs). Orthogonal FrequencyDivision Multiplexing (OFDM) is assumed as the DL transmission method.Each CCE includes a number of REs and the UEs are informed of the totalnumber of CCEs, N_(CCE), in a DL sub-frame through the transmission of aPhysical Control Format Indicator CHannel (PCFICH) by the NodeB. ThePCFICH indicates the number of OFDM symbols used for the PDCCHtransmission in the respective DL sub-frame.

For a Frequency Division Duplex (FDD) system, the UE determinesn_(PUCCH) as n_(PUCCH)=n_(CCE)+N_(PUCCH), where N_(CCE) is the first CCEof the respective DL SA and N_(PUCCH) is an offset configured by higherlayers, such as a Radio Resource Control (RRC) layer, and can beinformed to UEs through a DL broadcast channel.

A one-to-one mapping can exist between the PUCCH resources (PRB, CS,OCC) for HARQ-ACK signal transmission and the CCEs of the respective DLSA transmission. For example, if a single resource is used for HARQ-ACKsignal transmission, the single resource may correspond to the CCE withthe lowest index for the respective DL SA.

FIG. 5 illustrates a transmission of DL SAs using CCEs in respectivePDCCHs.

Referring to FIG. 5, a DL SA for UE1 uses CCEs 501, 502, 503, and 504, aDL SA for UE2 uses CCEs 511 and 512, a DL SA for UE3 uses CCEs 521 and522, and a DL SA for UE4 uses CCE 531. After cell-specific bitscrambling, modulation, and mapping to DL REs 540, each DL SA istransmitted in a PDCCH 550. Thereafter, UE1, UE2, UE3, and UE4 can userespectively n_(PUCCH)=0, n_(PUCCH)=4, n_(PUCCH)=6, and n_(PUCCH)=8 fortheir HARQ-ACK signal transmissions. Alternatively, if multiple CCEs areused to transmit a DL SA, HARQ-ACK information may be conveyed by themodulated HARQ-ACK signal and also by the selected PUCCH resource.

For a Time Division Duplex (TDD) system, multiple DL sub-frames may belinked to a single UL sub-frame in the sense that HARQ-ACK signaltransmissions from UEs in response to DL SA receptions in these multipleDL sub-frames will occur in the same UL sub-frame. This set of DLsub-frames will be referred to as bundling window. To avoid having toalways provision for the maximum PUCCH HARQ-ACK resources by alwaysassuming the maximum PDCCH size in each DL sub-frame in the bundlingwindow, the PUCCH resource indexing for HARQ-ACK signal transmission mayexploit possible variations in the PDCCH size among DL sub-frames.

Denoting the number of DL sub-frames in the bundling window by M, the DLsub-frame index by m=0, 1, . . . , M−1, the number of CCEs for a PCFICHvalue of p (N₀=0) by N_(p), and the first DL SA CCE in sub-frame m byn_(CEE)(m), a PUCCH resource indexing for HARQ-ACK signal transmissioncan be as described below. The UE first selects a value pε{0, 1, 2, 3}providing N_(p)≦n_(CCE) (m)<N_(p+1) and usesn_(PUCCH)=(M−m−1)×N_(p)+m×N_(p+1)+n_(CCE)(m)+N_(PUCCH) as the PUCCHresource for HARQ-ACK signal transmission in response to DL SA receptionin DL sub-frame m, where N_(p)=max{0,└[N_(RB) ^(DL)×(N_(sc)^(RB)×p−4)]/36┘}, N_(RB) ^(DL) is the number of PRBs in the DL operatingBW, and a CCE includes 36 REs.

The above indexing is based on interleaving the blocks of PUCCHresources for HARQ-ACK signal transmissions in an UL sub-frame that arelinked to blocks of CCEs located in the first, second, or third PDCCHOFDM symbol in respective DL sub-frames. Interleaving, instead of serialconcatenation of HARQ-ACK resources assuming the maximum PDCCH size ineach DL sub-frame, allows for savings in the PUCCH resources forHARQ-ACK signal transmissions, when the PDCCH size in some DL sub-framesis not the maximum.

FIG. 6 illustrates block interleaving of PUCCH resources when there are3 DL sub-frames in a bundling window.

Referring to FIG. 6, the PDCCH size is one OFDM symbol in the first DLsub-frame 610, three OFDM symbols in the second DL sub-frame 620, andtwo OFDM symbols in the third DL sub-frame 630. A total of 3N₁ PUCCHresources 640 are first reserved for the first PDCCH OFDM symbol foreach of the three DL sub-frames 640A, 640B, and 640C. Subsequently, atotal of 2N₂ PUCCH resources 650 are reserved for the second PDCCH OFDMsymbol of the second 650B and third 650C DL sub-frames. Finally, N₃PUCCH resources 660 are reserved for the third PDCCH OFDM symbol of thesecond 660B DL sub-frame.

In order to increase the supportable data rates in a communicationsystem, aggregation of multiple Component Carriers (CCs) is consideredin both the DL and the UL to provide higher operating BWs. For example,to support communication over 60 MHz, Carrier Aggregation (CA) of three20 MHz CCs can be used. A PDSCH reception in a DL CC is scheduled by arespective DL SA that is transmitted as illustrated in FIG. 5.

The transmission of HARQ-ACK signals associated with PDSCH receptions inmultiple DL CCs can be in the PUCCH of a single UL CC, which will bereferred to as a UL Primary CC (UL PCC) and can be UE-specific. Separateresources can be RRC configured in the UL PCC for HARQ-ACK signaltransmissions in response to DL SA receptions in multiple DL CCs.

FIG. 7 is a diagram illustrating resource allocation in an UL CC forHARQ-ACK signal transmissions corresponding to DL SAs received in 3 DLCCs.

Referring to FIG. 7, the HARQ-ACK signal transmissions corresponding toPDSCH receptions in 3 DL CCs, DL CC1 710, DL CC2 720, and DL CC3 730,occur in the UL PCC 740. The resources for HARQ-ACK signal transmissioncorresponding to DL SA receptions in DL CC1, DL CC2, and DL CC3 arerespectively in a first set 750, second set 760, and third set 770 ofPUCCH resources.

If the provisioned PUCCH resources for HARQ-ACK signal transmissionsconsider the maximum number of PDCCH CCEs, the resulting overhead can besubstantial. As a UE receiving PDCCH in a subset of DL CCs may not knowthe PDCCH size in other DL CCs, it may not know the number of respectivePUCCH resources. Consequently, the maximum number of PUCCH resources,corresponding to the maximum number of PDCCH CCEs in each DL CC, isassumed. If less than the maximum of PUCCH resources are used in asub-frame, the remaining PUCCH resources cannot typically be utilizedfor other transmissions, resulting in BW waste.

In addition to the PUCCH structure in FIG. 1, another PUCCH structurefor HARQ-ACK signal transmission in response to DL SA receptions inmultiple DL sub-frames (TDD) and/or in multiple DL CCs (CA) jointlycodes the O_(HARQ-ACK) HARQ-ACK information bits using, for example, ablock code such as the (32,O_(HARQ-ACK)) Reed-Mueller (RM) code.

FIG. 8 is a diagram illustrating a conventional PUCCH structure in onesub-frame slot using DFT Spread OFDM (DFT-S-OFDM) for the HARQ-ACKsignal transmission.

Referring to FIG. 8, after encoding and modulation, using respectively,for example, a (32, O_(HARQ-ACK)) RM block code punctured to a(24,O_(HARQ-ACK)) RM code and QPSK modulation (not shown), a set of thesame HARQ-ACK bits 810 is multiplied by a multiplier 820 with elementsof an OCC 830 and is subsequently DFT precoded 840. For example, for 5DFT-S-OFDM symbols per slot used for HARQ-ACK signal transmission, theOCC has a length of 5 and can be either {1, 1, 1, 1, 1}, or {1,exp(j2□/5), exp(j4□/5), exp(j6□/5), exp(j8□/5)}, or {1, exp(j4□/5),exp(j8□/5), exp(j2□/5), exp(j6□/5)}, or {1, exp(j6□/5), exp(j2□/5),exp(j8□/5), exp(j4□/5)}, or {1, exp(j8□/5), exp(j6□/5), exp(j4□/5),exp(j2□/5)}.

The output is passed through an IFFT 850 and is then mapped to aDFT-S-OFDM symbol 860. As the previous operations are linear, theirrelative order may be inter-changed. Because the HARQ-ACK signaltransmission in the PUCCH is assumed to be in one PRB, which includesN_(sc) ^(RB)=12 REs, 24 encoded HARQ-ACK bits are transmitted in eachslot with QPSK modulation (12 QPSK symbols). The same or differentHARQ-ACK bits may be transmitted in the second slot of the sub-frame.RSs are also transmitted in each slot using a CAZAC sequence 870, aspreviously described, to enable coherent demodulation of the HARQ-ACKsignals.

FIG. 9 illustrates a UE transmitter block diagram for the PUCCHstructure in FIG. 8.

Referring to FIG. 9, HARQ-ACK bits 905 are encoded and modulated by anencoder/modulator 910 and then multiplied by multiplier 920 with anelement of the OCC 925 for the respective DFT-S-OFDM symbol. After DFTpreceding by DFT 930, controller 950 selects the REs of the assignedPUCCH PRB and the sub-carrier mapper 940 maps the REs according to thecontrol signal from the controller 950. IFFT is performed by IFFT 960and a CP inserter 970 and a filter 980 insert a CP and filter thetransmitted signal 990, respectively.

FIG. 10 illustrates a NodeB receiver block diagram for the PUCCHstructure in FIG. 8.

Referring to FIG. 10, after an antenna receives the analog signal andfurther processing, a digital signal 1010 is filtered by filter 1020 andthe CP is removed by CP remover 1030. Subsequently, an FFT 1040 appliesFFT, a controller 1055 selects the REs used by the UE transmitter andthe sub-carrier demapper 1050 demaps the REs according to the controlsignal from the controller 1055. IDFT 1060 applies an IDFT, a multiplier1070 multiples the output from the IDFT 1060 with an OCC element 1075for the respective DFT-S-OFDM symbol, an adder 1080 sums the outputs forthe DFT-S-OFDM symbols conveying HARQ-ACK signals over each slot, and ademodulator/decoder 1090 demodulates and decodes the summed HARQ-ACKsignals over both sub-frame slots to obtain the transmitted HARQ-ACKbits 1095. Well known receiver functionalities such as channelestimation, demodulation, and decoding are not shown for brevity.

Although the PUCCH structure illustrated in FIG. 8 can support HARQ-ACKpayloads larger than a few bits, it still requires large PUCCH overheadas HARQ-ACK signal transmissions from at most 5 UEs (as determined bythe OCC length) can be accommodated per PRB. Unlike the PUCCH structureillustrated in FIG. 1, the HARQ-ACK signal transmission resource for thePUCCH structure illustrated in FIG. 8 cannot be implicitly determinedfrom PDCCH CCEs and is configured for each UE through RRC signaling. Asmost UEs do not usually have HARQ-ACK signal transmission in asub-frame, if the provisioned PUCCH resources accommodate a uniqueresource for each UE, the resulting overhead can be substantial, asunused resources cannot typically be utilized for other transmissions,resulting in BW waste.

Instead of having separate HARQ-ACK resources for each UE, HARQ-ACKresource compression may be applied to reduce PUCCH overhead in a ULPCC. However, even though HARQ-ACK resource compression reduces theprobability of resource waste, NodeB scheduler restrictions are requiredas collisions of HARQ-ACK resources should be avoided for UEs withshared HARQ-ACK resources.

Therefore, there is a need to reduce the PUCCH resources for HARQ-ACKsignal transmissions in response to DL SAs received in multiple DL CCsor multiple DL sub-frames.

There is another need to avoid collisions for HARQ-ACK signaltransmissions from multiple UEs that share the same set of PUCCHresources without imposing strict NodeB scheduler restrictions.

Finally, there is another need to determine rules for assigning PUCCHresources for HARQ-ACK signal transmissions from UEs.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been designed to solve at leastthe aforementioned limitations and problems in the prior art and provideat least the advantages described below.

An aspect of the present invention is to provide methods and apparatusfor a UE to transmit an HARQ-ACK signal in a UL CC, in response to thereception of multiple DL SAs transmitted by a NodeB in multiple DL CCsor multiple DL sub-frames. The UL CC and a first DL CC establish thecommunication link when the UE is configured communication over a singleUL CC and a single DL CC.

In accordance with an aspect of the present invention, a method fortransmitting an acknowledgement signal at a UE in a time division duplex(TDD) wireless communication system includes receiving first controlinformation on a first downlink component carrier (DL CC), the firstcontrol information including a first downlink assignment index (DAI)and a first transmission power command (TPC), receiving second controlinformation on either the first DL CC or a second DL CC, the secondcontrol information including a second DAI and a second TPC, determininga power for a transmission of the acknowledgement signal based on avalue of the first TPC if a value of the first DAI is equal to apredetermined value, determining a resource for a transmission of theacknowledgement signal based on a value of the second TPC if the secondcontrol information is received on the first DL CC and a value of thesecond DAI is greater than the predetermined value, and transmitting theacknowledgement signal on the resource using the determined power,wherein the value of the second TPC is used for determining the resourcefor the transmission of the acknowledgement signal regardless of thevalue of the second DAI if the second control information is received onthe second DL CC.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of the presentinvention will be more apparent from the following detailed descriptiontaken in conjunction with the accompanying drawings, in which:

FIG. 1 is a diagram illustrating a conventional PUCCH sub-framestructure for an HARQ-ACK signal transmission;

FIG. 2 is a diagram illustrating an HARQ-ACK signal transmission in asub-frame slot for a PUCCH structure as illustrated in FIG. 1;

FIG. 3 is a block diagram illustrating a transmitter for a PUCCHstructure as illustrated in FIG. 1;

FIG. 4 is a block diagram illustrating a receiver for a PUCCH structureas illustrated in FIG. 1;

FIG. 5 is a diagram illustrating a transmission of a DL SA using CCEs ina PDCCH;

FIG. 6 is a diagram illustrating block interleaving of PUCCH resourcesassuming a Time Division Duplex system with 3 DL sub-frames in abundling window;

FIG. 7 is a diagram illustrating resource allocation in a UL CC forHARQ-ACK signal transmissions corresponding to DL SAs received in 3 DLCCs;

FIG. 8 is a diagram illustrating a conventional PUCCH structure in onesub-frame slot using DFT Spread OFDM for the HARQ-ACK signaltransmission;

FIG. 9 is a block diagram illustrating a transmitter for a PUCCHstructure as illustrated in FIG. 8;

FIG. 10 is a block diagram illustrating a receiver for a PUCCH structureas illustrated in FIG. 8;

FIG. 11 is a diagram illustrating a transmission of 3 DL SAs in a DL PCCand a mapping of the respective 3 resources available for a transmissionof an HARQ-ACK signal, according to an embodiment of the presentinvention;

FIG. 12 is a diagram illustrating a restriction that UEs having a sameDL PCC are activated (and deactivated) DL SCCs in a same order,according to an embodiment of the present invention;

FIG. 13 is a diagram illustrating an ordering of activation anddeactivation for 5 DL CCs depending on the DL CC used for thetransmission of the respective DL SAs, according to an embodiment of thepresent invention;

FIG. 14 is a diagram illustrating use of a TPC IE in a first ordered DLSA, as determined by a DAI IE value, to provide a TPC command for anHARQ-ACK signal transmission and use of a TPC IE in remaining DL SAs toprovide an index for a respective resource for the HARQ-ACK signaltransmission, according to an embodiment of the present invention;

FIG. 15 is a block diagram illustrating a transmitter for a PUCCHstructure where a resource for an HARQ-ACK signal transmission isindexed by a TPC IE value in a DL SA, other than a first ordered DL SA,as determined from a value of a DAI IE, according to an embodiment ofthe present invention;

FIG. 16 is a block diagram illustrating a receiver for a PUCCH structurewhere a resource for an HARQ-ACK signal reception is indexed by a TPC IEvalue in a DL SA, other than a first ordered DL SA, as determined from avalue of a DAI IE, according to an embodiment of the present invention;and

FIG. 17 is a diagram illustrating a resource mapping for an HARQ-ACKsignal transmission for 2 DL CCs, each transmitting its own DL SA, usinga DL CC specific offset, according to an embodiment of the presentinvention.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

Various embodiments of the present invention will be described in moredetail below with reference to the accompanying drawings. The presentinvention may, however, be embodied in many different forms and shouldnot be construed as limited to the embodiments set forth herein. Rather,these embodiments are provided so that this disclosure will be thoroughand complete and will fully convey the scope of the invention to thoseskilled in the art.

Additionally, although the present invention is described for acommunication system using DFT-S-OFDM or Single-Carrier FrequencyDivision Multiple Access (SC-FDMA) transmission, it also generallyapplicable to other Frequency Division Multiplexing (FDM) transmissionsincluding OFDM.

Methods and apparatuses are described for a UE to determine the PUCCHresource for HARQ-ACK signal transmission, in response to multiple DL SAreceptions in multiple DL CCs or in multiple DL sub-frames.

In accordance with an embodiment of the present invention, PUCCHresources are indexed for HARQ-ACK signal transmission in a UL PCC(herein referred to as HARQ-ACK resources). The HARQ-ACK resources maybe RRC-configured to a UE (for example, using the PUCCH structure asillustrated in FIG. 8) or may be dynamically determined by a UE usingthe indexes of the CCEs for the respective DL SAs (for example, usingthe PUCCH structure as illustrated in FIG. 1).

Herein, the HARQ-ACK signal transmission in the PUCCH is assumed to bebased on the following two principles:

1. A single UE-specific UL CC (UL PCC) is RRC-configured for theHARQ-ACK transmission in the PUCCH for a UE configured multiple DL CCs.

2. For a UE configured single UL/DL carrier-pair operation in FDD andreceiving a DL SA in a single DL sub-frame in the DL PCC in TDD, theHARQ-ACK resource is implicitly derived from the CCEs of the respectiveDL SA, as it was previously described.

RRC-configured CCs can be activated or deactivated, for example bymedium access control signaling. Herein, activation of a DL (or UL) CCmeans that the UE can receive PDSCH (or transmit PUSCH) in that CC.Similarly, the reverse applies for deactivation of a DL (or UL) CC. Tomaintain communication, one DL CC remains activated and is referred toas a DL Primary CC (DL PCC). The remaining DL CCs are referred to as DLSecondary CCs (DL SCCs). The DL PCC is assumed to be linked to the ULPCC and both are UE-specific.

For HARQ-ACK resource mapping in the UL PCC, the following two casesexist for a UE having communication in multiple DL CCs:

-   -   1. All DL SAs scheduling PDSCH in the multiple DL CCs are        transmitted in the DL PCC.    -   For example, in heterogeneous network operation with 2 DL CCs        and 2 UL CCs.    -   2. Some DL SAs scheduling PDSCH in multiple DL CCs are not        transmitted in the DL PCC.    -   For example, parallelizing the nominal operation with a single        UL/DL carrier pair.

Using a PUCCH structure as illustrated in FIG. 1, in accordance with anembodiment of the present invention, HARQ-ACK resource mapping dependson whether the first or the second of the previous two cases applies.For the first case, HARQ-ACK resource mapping rules used for a FDDsystem with a single DL/UL CC pair are generalized and expanded. For thesecond case, the HARQ-ACK resource mapping rules used for a TDD systemwith a single UL/DL CC pair are generalized and expanded, subject toadditional conditions.

For the first case (all DL SAs are transmitted in the DL PCC), assumingthat a UE receives M DL SAs for respective PDSCH receptions in M DL CCs,and denoting the first CCE for each of the M DL SAs as n_(CCE)(m), n=0,1, . . . , M−1, the resource available for the HARQ-ACK signaltransmission in response to PDSCH reception in DL CC m is determined asshown in Equation (1).

n _(PUCCH)(m)=n _(CCE)(m)+N _(PUCCH) , m=0,1, . . . ,M−1  (1)

FIG. 11 illustrates a transmission of three DL SAs in a DL PCC of a UEand mapping three respective HARQ-ACK resources.

Referring to FIG. 11, DL SA 1 1110 includes 2 CCEs 1111 and 1112, wherethe first CCE 1111 maps to a first HARQ-ACK resource (RSRC) 1140. DL SA2 1120 includes 4 CCEs 1121, 1122, 1123, and 1124, where the first CCE1121 maps to a second HARQ-ACK resource (RSRC) 1150. DL SA 3 1130includes 2 CCEs 1131 and 1132, where the first CCE 1131 maps to a thirdHARQ-ACK resource (RSRC) 1160.

For the second case (some DL SAs to a UE are not transmitted in the DLPCC), there is a restriction that UEs having the same DL PCC areactivated (and deactivated) DL SCCs in the same order which isconfigured by RRC signaling.

FIG. 12 is a diagram illustrating a restriction that UEs having a sameDL PCC are activated (and deactivated) DL SCCs in a same order,according to an embodiment of the present invention.

Referring to FIG. 12, UEs with DL CC2 1210 as a DL PCC are activated(and deactivated) DL SCCs in the same order, for example, starting withDL CC3 1220, and then continuing with DL CC4 1230, DL CC5 1240, and DLCC1 1250. UEs having DL CC 2 as DL PCC can have a different number ofactivated DL SCCs. Then, as a UE decodes the PCFICH in its activated DLCCs, it can identify the corresponding reserved HARQ-ACK resources fromthe PDCCH size. This restriction applies only for DL SCCs having PDCCHtransmissions.

FIG. 13 is a diagram illustrating an ordering of activation anddeactivation for 5 DL CCs depending on the DL CC used for thetransmission of the respective DL SAs, according to an embodiment of thepresent invention.

Referring to FIG. 13, for a reference UE, DL CC2 (DL PCC) 1310 conveysDL SAs for DL CC2 1310A, DL CC3 1310B, and DL CC4 1310C. DL CC5 1320conveys DL SAs for DL CC5 1320A. DL CC1 1330 conveys DL SAs for DL CC11330A. Because scheduling in DL CC3 and DL CC4 is through DL SAstransmitted in DL CC2 (for example, an index in the DL SA can indicatethe DL CC), DL CC3 and DL CC4 can be activated (and deactivated) in anyorder. However, this is not the case for DL CC5 and DL CC1, which areactivated (and deactivated) in the same order for all UEs having DL CC2as their DL PCC. Moreover, the HARQ-ACK signal transmissions in responseto DL SA receptions in DL CC5 and DL CC1 is not in the UL CC(s) linkedto these DL CCs, but are in the UL PCC (which linked to the DL PCCassumed to be DL CC2).

HARQ-ACK resource mapping will now be described below, assuming theprevious restriction and considering for simplicity DL CCs of the sameBW.

Herein, M is the number of activated DL SCCs for a UE with DL SAtransmissions to that UE, m 0, 1, . . . , M−1 is the index of the DL SCCin the set of M activated DL CCs, N_(p) is the number of CCEs for aPCFICH value of p (where N₀=0), and n_(CCE) (m) is the first CCE in theDL SA scheduling PDSCH in DL SCC m.

The UE first selects a value pε{0, 1, 2, 3} that providesN_(p)≦n_(CCE)(m)<N_(p+1) and uses Equation (2) as the HARQ-ACK resourcecorresponding to PDSCH in DL SCC m.

n _(PUCCH)(m)=(M−m−1)×N _(p) +m×N _(p+1) +n _(CCE)(m)+N _(PUCCH) , m=0,. . . ,M−1  (2)

For DL SAs transmitted in the DL PCC, the HARQ-ACK resource mapping isas described in Equation (1).

For M=4 activated DL SCCs with DL SA transmission to a UE, with each DLSCC having maximum PDCCH size of 3 OFDM symbols, N_(RB) ^(DL)=100 PRBs,N_(sc) ^(RB)=12 REs, and 36 REs per CCE, the maximum number of CCEs in aPDCCH is 87 and the HARQ-ACK resource indexing corresponding to PDSCHreception in DL SCC m=0, 1, . . . , M−1 is given in Table 2.

TABLE 2 HARQ-ACK resource in DL SCC m n_(CCE) < 22 22 ≦ n_(CCE) < 55 55≦ n_(CCE) < 88 m = 0 n_(PUCCH) ⁽¹⁾ = n_(CCE) + N_(PUCCH) ⁽¹⁾ n_(PUCCH)⁽¹⁾ = 66 + n_(CCE) + N_(PUCCH) ⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 154 + n_(CCE) +N_(PUCCH) ⁽¹⁾ m = 1 n_(PUCCH) ⁽¹⁾ = 22 + n_(CCE) + N_(PUCCH) ⁽¹⁾n_(PUCCH) ⁽¹⁾ = 88 + n_(CCE) + N_(PUCCH) ⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 187 +n_(CCE) + N_(PUCCH) ⁽¹⁾ m = 2 n_(PUCCH) ⁽¹⁾ = 44 + n_(CCE) + N_(PUCCH)⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 121 + n_(CCE) + N_(PUCCH) ⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 220 +n_(CCE) + N_(PUCCH) ⁽¹⁾ m = 3 n_(PUCCH) ⁽¹⁾ = 66 + n_(CCE) + N_(PUCCH)⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 154 + n_(CCE) + N_(PUCCH) ⁽¹⁾ n_(PUCCH) ⁽¹⁾ = 253 +n_(CCE) + N_(PUCCH) ⁽¹⁾

The previous HARQ-ACK resource mapping for multiple DL CCs follows theprinciples of HARQ-ACK resource mapping in TDD systems with a singleDL/UL carrier. However, as no HARQ-ACK resource compression is used, themaximum number of HARQ-ACK resources in the UL PCC can be very large.For example, using Table 2 for the previous setup, the maximum HARQ-ACKresources in the UL PCC for M=5 DL CCs can be computed asn_(PUCCH)=253+n_(CCE) N_(PUCCH). Neglecting N_(PUCCH), as it is only anoffset, and assuming the maximum value of n_(CCE)=87 for N_(RB)^(DL)=100 PRBs, the maximum number of HARQ-ACK resources in the UL PCCis 253+87=340. Assuming a maximum multiplexing capacity of 18 HARQ-ACKchannels per PRB, about 19 PRBs are used to accommodate HARQ-ACKtransmissions in the PUCCH of the UL PCC. This represents 19% of thetotal UL PCC resources. Moreover, as the DL PCC is not considered toparticipate in the HARQ-ACK resource mapping for DL SCCs having DL SAtransmission (for example, the DL PCC may also support UEs configuredwith a single DL/UL CC pair), NodeB scheduler restrictions are used toavoid collisions of HARQ-ACK resources.

To reduce the HARQ-ACK resources required to support communication overmultiple DL CCs (for the second of the previous cases), in accordancewith an embodiment of the present invention, for DL SAs scheduling PDSCHtransmissions in DL SCCs, the NodeB scheduler can prioritize theplacement of the first CCE to be within the first 22 CCEs (for the setupin Table 2). As the number of UEs scheduled in multiple DL CCs persub-frame is typically small, the impact of this prioritization on theoverall CCE availability is minor. Further, assuming that the CCEs aredivided into CCEs that exist only in a UE-Common Search Space (UE-CSS)and CCEs that exist in a UE-Dedicated Search Space (UE-DSS), CCEscorresponding to the UE-CSS in DL SCCs can be omitted from thecalculation of n_(CCE). Then, a maximum of about 88+22=110 HARQ-ACKresources will be used and, with 18 HARQ-ACK channels per PRB, about 6PRBs in the UL PCC suffice. This represents about 6% maximum overhead tosupport HARQ-ACK transmissions, for all UEs. Such an overhead istolerable and comparable to the maximum overhead of about 5 PRBs whenUEs are configured only a single DL/UL CC pair.

When HARQ-ACK resources (for the second of the previous cases) areconfigured by RRC signaling to a UE having communication over multipleDL CCs, additional HARQ-ACK resource overhead occurs due to theprovision for the maximum HARQ-ACK resources for all UEs configuredmultiple DL CCs, regardless of whether these UEs are scheduled in asub-frame. In peak conditions for DL CA support, the overhead due toHARQ-ACK resource allocation by RRC signaling may increase significantlywhile only modest increases can occur with dynamic HARQ-ACK resourceallocation. HARQ-ACK resource sharing among multiple UEs can alleviatethe increased overhead with HARQ-ACK resource allocation through RRCsignaling, but such sharing imposes NodeB scheduler restrictions, as UEssharing the same HARQ-ACK resource cannot have a DL SA in the samesub-frame.

In accordance with another embodiment of the present invention HARQ-ACKresource compression is enabled. For example, HARQ-ACK overheadreduction may be achieved through NodeB scheduler restrictions byplacing the first CCE of the respective DL SAs for DL SCCs in the first22 CCEs (for the previous example). The scheduler will also then ensurethat no DL SA in the DL PCC has a first CCE given asn_(CCE,1)=22·m+n_(CCE)(m), m=0, . . . , M−1

Alternatively, the same resource mapping for all DL CCs can be used forthe HARQ-ACK signal transmission in the UL PCC andn_(PUCCH)(m)=n_(CCE)(m)+N_(PUCCH), m=0, 1, . . . , M−1. Thereafter, thescheduler then ensures that n_(CCE) (m), m=0, 1, . . . , M−1 isdifferent among all DL CCs where a UE receives DL SA.

To avoid having such constraints on the NodeB scheduler, an offset forthe HARQ-ACK resource can be provided by the respective DL SA. Thecorresponding Information Element (IE) in the DL SA will be referred toas HARQ-ACK Resource Index (HRI) IE. Denoting the HRI IE value for DLSCC m as HRI(m), the HARQ-ACK resource corresponding to PDSCH in DL SCCm is obtained as

n _(PUCCH)(m)=(M−m−1)×N _(p) +m×N _(p+1) +n _(CCE) +N _(PUCCH) +HRI(m),m=0, . . . ,M−1  (3)

For example, assuming that HRI IE consists of 2 bits, its interpretationcan be as in Table 3.

TABLE 3 Mapping the HRI to an HARQ-ACK Resource Offset Value. HARQ-ACKResource Index Field Offset Value 00 0 01 −1 10 1 11 2

The HRI IE can also be used to avoid having the constraint that thefirst CCE the NodeB scheduler uses to transmit DL SAs in DL SCCs iswithin the first 22 CCEs (with or without accounting for CCEs allocatedto the UE-CSS), that is n_(CCE)(m)<22, m=0, . . . M−1. Instead, the CCEindex associated with the HARQ-ACK resource can be defined using themodulo operation with respect to a maximum CCE index value, N_(CCE)^(max), and n_(PUCCH) (m) as shown in Equation (4).

n _(PUCCH)(m)=((M−m−1)×N _(p) +m×N _(p+1) +n _(CCE)(m))mod(N _(CCE)^(max))+N _(PUCCH) +HRI(m), m=0, . . . ,M−1  (4)

The value of N_(CCE) ^(max) can be either signaled by the NodeB (RRCsignaling or broadcast signaling) or be predefined. The modulo operationbetween two integers, x, y with y>0, is defined as x mod(y)=x−n·y, wheren=└x/y┘.

In general, the HARQ-ACK resource corresponding to the PDSCH in DL CC mcan be determined as a function of the first CCE used for the respectiveDL SA and the value of the HRI IE as shown in Equation (5).

n _(PUCCH)(m)=f(n _(CCE)(m),HRI(m)), m=0,1, . . . ,M−1  (5)

For example, the HARQ-ACK resource in response to DL SA reception in DLCC m can be determined as shown in Equation (6).

n _(PUCCH)(m)=n _(CCE)(m)+HRI(m)+N _(PUCCH) , m=0,1, . . . ,M−1  (6)

To further alleviate HARQ-ACK resource collisions, a DL CC specificoffset N_(HARQ-ACK) (m), m=0, 1, . . . , M−1 can be introduced, forexample by RRC signaling, and n_(PUCCH) (m), as shown in Equation (7).

n _(PUCCH)(m)=n _(CCE)(m)+HRI(m)+N _(HARQ-ACK)(m)+N _(PUCCH) , m=0,1, .. . ,M−1  (7)

Similarly, for the HARQ-ACK resource indexing in Equation (4),n_(PUCCH)(m) can be determined, as shown in Equation (8).

n _(PUCCH)(m)=((M−m−1)×N _(p) +m×N _(p+1) +n _(CCE)(m))mod(N _(CCE)^(max))+N _(PUCCH) +HRI(m)+N _(HARQ-ACK)(m), m=0, . . . ,M−1  (8)

The addition of an explicit HRI IE in the DL SAs can be avoided if anexisting IE can be interpreted as providing the HRI. Assuming that DLSAs include a Downlink Assignment Index (DAI) IE that provides a countfor the DL SA number, the DL SAs can be ordered.

For example, assuming that a UE can receive DL SAs in DL CC1, DL CC2, DLCC3, and DL CC4 and that the NodeB transmits DL SAs to the UE in DL CC1,DL CC2, and DL CC4, the DAI IE in the DL SAs can have a value of 1 forDL CC2, a value of 2 for DL CC4, and a value of 3 for DL CC1.Accordingly, the UE identifies that the DL SA in DL CC2 is orderedfirst, the DL SA in DL CC4 is ordered second, and the DL SA in DL CC1 isordered third. In a similar manner, for a TDD system with a single ormultiple CCs and, for example, 4 DL sub-frames in the bundling window,the DAI IE can indicate whether the DL SA the UE receives in a sub-frameis the first, second, third, or fourth transmitted DL SA for the givenCC.

DL SAs are also assumed to include a Transmission Power Control (TPC) IEproviding TPC commands in order for the UE to adjust the HARQ-ACK signaltransmission power. It is assumed herein that all DL SAs include the TPCIE. However, because the HARQ-ACK signal transmission is only in the ULPCC, a single TPC command can suffice. In accordance with an embodimentof the present invention, a TPC command is provided by the TPC IE in thefirst DL SA, as determined by the DAI IE value. The TPC IEs in theremaining DL SAs can be used as HRI IEs.

FIG. 14 illustrates a principle of identifying and using the bits of anIE in the DL SAs to index the resources for the HARQ-ACK signaltransmission according to an embodiment of the present invention.Although FIG. 14 considers the TPC IE, an explicit HRI IE may be usedinstead.

Referring to FIG. 14, a TPC IE in a first ordered DL SA 1410 (asdetermined by the DAI IE value) provides a TPC command for a HARQ-ACKsignal transmission 1420 in response to reception of DL SAs. Each TPC IEin the remaining DL SA2 1430 through DL SA K 1450 is used as an indexfor HARQ-ACK resources 1440 through 1460, respectively.

Although dynamically indexed HARQ-ACK resources are considered, the HRIfunctionality is independent of how the HARQ-ACK resource is determinedand serves to further index the HARQ-ACK resources in order to avoidcollisions when resource compression is applied to the HARQ-ACK resourcemapping. Moreover, the HRI functionality is applicable to either a PUCCHstructure as illustrated in FIG. 1 or a PUCCH structure as illustratedin FIG. 8 and to further indexing either dynamically determined orRRC-configured HARQ-ACK resources.

If the first DL SA (with DAI=1) is missed by the UE, the TPC command forthe HARQ-ACK transmission is missed and the UE does not perform arespective power adjustment. However, this is not expected to have anoticeable impact on the overall system operation as it is a lowprobability event, as UEs with DL CA have good link quality and DL SAsare unlikely to be missed, and the TPC adjustment is typically small. Itis noted that if only the DL SA with DAI=1 is received by the UE (eitherin the DL PCC for FDD or in the first sub-frame of the DL PCC for TDD),the HARQ-ACK resource is implicitly derived from the CCEs of therespective DL SA (second principle for the HARQ-ACK signal transmissionassumed by the invention).

FIG. 15 is a block diagram illustrating a transmitter for a HARQ-ACKsignal in a PUCCH where a resource for the HARQ-ACK signal transmission(HARQ-ACK resource) is indexed by a TPC IE value in a DL SA, other thana first ordered DL SA, as determined from a value of a DAI IE, accordingto an embodiment of the present invention. In FIG. 15, the maincomponents are the same as those illustrated in FIG. 3 and describedabove, with the exception that the HARQ-ACK resource depends on anoffset specified by a HRI value controller 1510 for mapping the TPC IE(or of the HRI IE) value, which the UE obtains from the respective DLSAs (with DAI IE value larger than one in the DL PCC) and uses to derivethe HARQ-ACK resource. The HARQ-ACK resource includes the CS which isapplied by the CS mapper 1520 and the PRB which is determined by the PRBselection controller 1530 (and also the OCC—not shown for simplicity).The transmitter structure as illustrated in FIG. 9 may be modified inthe same manner.

FIG. 16 is a block diagram illustrating a receiver for a HARQ-ACK signalin a PUCCH where a resource for the HARQ-ACK signal reception (HARQ-ACKresource) is indexed by a TPC IE value in a DL SA, other than a firstordered DL SA, as determined from a value of a DAI IE, according to anembodiment of the present invention. In FIG. 16, the main components arethe same as those illustrated in FIG. 4 and described above, with theexception that the HARQ-ACK resource depends on the offset specified bythe HRI value controller 1610 for the mapping of the TPC IE (or of theHRI IE) value, which the NodeB included in the respective DL SA. Theresource includes the CS which is applied by the CS demapper 1630 andthe PRB which is determined by PRB selection controller 1620 (and alsothe OCC—not shown for simplicity). The receiver structure as illustratedin FIG. 10 may also modified in the same manner.

FIG. 17 is a diagram illustrating a resource mapping for an HARQ-ACKsignal transmission for 2 DL CCs, each transmitting its own DL SA, usinga DL CC specific offset, according to an embodiment of the presentinvention.

Referring to FIG. 17, an outer BW region, starting from PRB 0 1710, isused for PUSCH transmissions and PUCCH transmissions other than dynamicHARQ-ACK transmissions 1720 (dynamic HARQ-ACK transmissions are inresponse to receptions of DL SAs). After N_(PUCCH) HARQ-ACK resources1730, corresponding, for example, to N_(PUCCH)/18 PRBs (assuming 18HARQ-ACK channels per PRB), the HARQ-ACK resources in response to DL SAsin the DL PCC are mapped 1740. After N_(PUCCH)+N_(HARQ-ACK) (0) HARQ-ACKresources 1750, corresponding, for example, to (N_(PUCCH)+N_(HARQ-ACK)(0))/18 PRBs, the HARQ-ACK resources in response to DL SAs in the DL SCCare mapped 1760. The HARQ-ACK resources for DL SAs in the DL PCC and forDL SAs in the DL SCC may partially or completely overlap (for example,complete overlapping occurs for n_(CCE)(m)=n_(CCE) and N_(HARQ-ACK)(m)=0 in Equation (7)). Finally, resources allocated to other PUCCH orPUSCH transmission follow 1770. The same mapping can apply from theother end of the BW (although not shown for brevity).

While the present invention has been shown and described with referenceto certain embodiments thereof, it will be understood by those skilledin the art that various changes in form and details may be made thereinwithout departing from the spirit and scope of the present invention asdefined by the appended claims and their equivalents.

What is claimed is:
 1. A method for transmitting an acknowledgementsignal at a user equipment (UE) in a time division duplex (TDD) wirelesscommunication system, the method comprising: receiving first controlinformation on a first downlink component carrier (DL CC), the firstcontrol information including a first downlink assignment index (DAI)and a first transmission power command (TPC); receiving second controlinformation on either the first DL CC or a second DL CC, the secondcontrol information including a second DAI and a second TPC; determininga power for a transmission of the acknowledgement signal based on avalue of the first TPC if a value of the first DAI is equal to apredetermined value; determining a resource for a transmission of theacknowledgement signal based on a value of the second TPC if the secondcontrol information is received on the first DL CC and a value of thesecond DAI is greater than the predetermined value; and transmitting theacknowledgement signal on the resource using the determined power,wherein the value of the second TPC is used for determining the resourcefor the transmission of the acknowledgement signal regardless of thevalue of the second DAI if the second control information is received onthe second DL CC.